To boost your immune system you need to take at least a thousand units of C a day, and more when sick.
You also need to take several thousand--yes, several thousand units of D a day. The amount of 400 units a day that is normally recommended is actually a minimal amount, but docs who really know about Vit D recommend several thousand units a day, some say as much as 8000. I take at least 4 or 5 thousand units a day, and haven't had a cold since I started taking so much.
Also make sure you get enough zinc, but not too much, as high levels are toxic.
Take turmeric/curcumin tablets or capsules in double the recommended dose, as again, the amount recommended is too low. This stuff is good for the immune system.
Take Airborne, which comes in several forms--a powder to dissolve in water, a large tablet to dissolve in water, or a large chewable gummy thing. I prefer the gummy chew, as the stuff which makes the tablets dissolve in water also dissolves bones and teeth.
Airborne is a combination of immune supporting vitamins and herbs that was developed by a teacher who got fed up with constantly getting all the colds, flu, and other illnesses brought to school by the kids.
In addition to these supplements, also eat mostly healthy, get some moderate exercise, and get plenty of sleep.
If you do feel a cold or flu comming on, increase the doses of Airborne, turmeric/curcuming, vit C, & vit D, but don't increase the dose of the zinc, as that is a mineral that can be harmful in larger doses.
Hope this helps.
_________________
If a man does not keep pace with his companions, perhaps it is because he hears a different drummer.
Let him step to the music which he hears, however measured, or far away.--Henry David Thoreau